restructured gridcreators

dune/vtk/CMakeLists.txt

dune/vtk/datacollectors/structureddatacollector.hh

dune/vtk/filereader.hh

dune/vtk/filewriter.hh

dune/vtk/forward.hh

dune/vtk/gridcreator.hh

dune/vtk/gridcreatorinterface.hh

dune/vtk/gridcreators/CMakeLists.txt

dune/vtk/gridcreators/common.hh

dune/vtk/gridcreators/continuousgridcreator.hh

dune/vtk/gridcreators/derivedgridcreator.hh

dune/vtk/gridcreators/discontinuousgridcreator.hh

dune/vtk/gridcreators/parallelgridcreator.hh

dune/vtk/gridcreators/serialgridcreator.hh

dune/vtk/pvdwriter.hh

dune/vtk/vtkreader.hh

dune/vtk/vtkreader.impl.hh

dune/vtk/vtktimeserieswriter.hh

dune/vtk/vtkwriter.hh

dune/vtk/vtkwriterinterface.hh